I too never owned a diesel before, but I am interested to learn more about the 2.2D because it will be awesome to drive.
So many of you get the GT, paying a premium for features you think are awesome which others think are unnecessary or hard to justify. Well, being rewarded daily with copious amount of torque, exactly where needed, are enough reason to me to pay a premium for. Yes, it is not faster 0-60, but I don't really care about 0-60 and the diesel has a huge torque advantage.
I am not too concerned about maintenance cost, I don't think it will be much different for the ~8 years I am going to own it. Checking oil level, even for the 2.5L, is recommended on every fuel-up, and it seems Mazda has addressed the oil-rise issue on earlier motors.
That said, it depends on how much more I'd need to pay and what extras I don't need I'd be forced to get.
In addition, diesel might not be good for people with mostly short trips.
Here, diesel is typically a little bit extra, maybe 7%, but it seems today it is about the same as 87.
Mazda's ended-up using a urea tank for the US version, though I have heard it is smaller, since not much after treatment is necessary, as the engine is already pretty clean. It is therefore my educated guess that the cost for DEF will be insignificant compared with the total cost of fuel.